Since the implant of the first cardiac valvular prosthesis in the anatomic position in 1960, more than 50 different cardiac valves have been introduced over the last forty years. Unfortunately, after years of development of mechanical and tissue valves there remain significant problems associated with both types of valves.
Mechanical vs. Tissue Valves
Mechanical valves are durable in patients but require long-term anticoagulation therapy. Tissue valves offer freedom from anticoagulation therapy and the problems of bleeding, but tend to degenerate rapidly, particularly in younger patients. The most commonly implanted tissue valves are constructed from chemically-treated animal tissues (i.e., glutaraldehyde-fixed pericardial or porcine valves). The preservation, sterilization, and fixation processes currently used in tissue valve preparation are believed to contribute to the lack of longevity of tissue valves.
Ross Procedure
One alternative approach for aortic valve replacement has been to transpose the patient's own pulmonary valve into the aortic position in the same individual, as described by Ross in the late 1960's. Although a technically demanding procedure, the Ross procedure frees the patient from anticoagulation therapy and has substantial longevity compared to other types of tissue valves. A disadvantage of using the pulmonary valve to replace the aortic valve in the same patient is that the pulmonary valve must also be replaced. Most commonly, the replacement tissue for the excised pulmonary valve is a valve (aortic or pulmonic) derived from a cadaver (“homograft”). Problems arise from lack of donor availability and size mismatches between the donor homograft and the living recipient. Unfortunately, replacing the pulmonary valve with a homograft is associated with immunologically-mediated stenosis in some patients which limits their longevity.
Monocusp Procedure
Alternatively, a single flap of tissue from the pulmonary trunk has been used to create a pulmonary “mono-cusp” valve in pediatric patients undergoing the Ross procedure. Long-term function of the monocusp valve has yet to be documented. Historically, it is known that a single leaflet valve design has a less efficient closure than a tri-leaflet valve. The suboptimal function of a monocusp valve may adversely impact long-term results. It is a drawback that the mono-cusp procedure is restricted to replace a valve at the location where the tissue flap is created. The monocusp procedure does not provide a source for replacement of valves other than the pulmonary valve.
Trileaflet Valve Derived from Pulmonary Artery Tissue
Another previously described method to replace the aortic valve entails surgical reconstruction of a tube of tissue from the pulmonary artery of the same individual. In this procedure, a tube of tissue was harvested from the pulmonary trunk and reconfigured into a trileaflet valve. In order to create a valve, the base of the pulmonary tissue tube was sutured to the aortic annulus and to the aortic wall at three points. This procedure was attempted in three pediatric patients and abandoned due to immediate and severe aortic insufficiency in two patients. The failure of this valve replacement procedure resulted, in part, from the extreme technical challenge for the surgeon. In this procedure, the surgeon must simultaneously construct and implant the valve while attempting to surgically compensate for any size discrepancies between the donor tissue and the recipient valve site.
As described previously, promising attempts to create a tissue valve by reconfiguring an individual's own living tissues have been problematic. It would be advantageous to have a method to more efficiently, effectively, and reliably construct a functional and durable tissue valve. It would be desirable for the valve to be a non-immunogenic structure capable of cellular regeneration and repair.
U.S. Pat. No. 5,713,950, issued to Cox discloses a valve constructed from a tubular structure. This invention is a nesting of tubes dependent on multiple suture lines or points to join the tubes to create a valvular structure. It is a drawback that these sutures are positioned in areas of high stress during the function of the valve through the cardiac cycle. Although this valve is a simple design, it would be inefficient and difficult to use this method to reconfigure the patient's own tissues into a valvular structure.
U.S. Pat. No. 6,494,909, issued to Greenhalgh, discloses a device and means for a braided valve and minimally invasive deployment. The invention does not describe the area of attachment of the leaflets to the walls of the tubular structure to create a functional three-dimensional tri-leaflet valve. This invention does not describe a means for creating an autologous or living tissue valve. It is a further disadvantage that this invention describes that it is placed in a catheter for deployment. This is distinguished from other braided structures which are deployed by an internal mechanism with the potential for more maneuverable and narrower insertion profiles (such as that disclosed in Patent Cooperation Treaty application (designating the U.S.) No. PCT/US02/40349, filed Dec. 16, 2002, entitled “DYNAMIC CANNULA,” and commonly assigned to the assignee of the present invention, the disclosure of which application is incorporated herein by reference in its entirety).